Known LED displays include a plurality of light emitting diodes (LEDs) arranged in a square-array manner, and display video information by controlling blinks of the individual LEDs.
A technical development and a cost reduction of the LEDs achieve various uses of the LED displays, including a use for indoor-and-outdoor advertisement display. These LED displays have mainly displayed dynamic images, such as nature images and animated images. With respect to indoor use, a shortened pitch of pixels has achieved a shorter distance of vision. Consequently, the LED displays have been used to display images of personal computers used in conference rooms or used for monitor. With respect to the monitor use in particular, the LED displays have increasingly displayed nearly static images of the personal computers.
The mainstream of such an LED display is a surface-mount-device (SMD) LED display that includes a small LED package mounted on a substrate, the LED package including the LEDs placed within a ceramic or resin cavity, and fixed from thereabove with a resin sealant. The SMD LED display has been mainly used as a large display with a pixel pitch of 3 mm or more.
The LEDs have been manufactured at lower cost and have been received a demand for a higher precision of the manufacture. In view of this, products having a small pixel pitch of, for instance, about 1.9 mm or 1.5 mm are on the market. Further, in order for the LEDs to be more precise, a chip-on-board (COB) LED display is used that includes LEDs with no shell directly mounted on the substrate instead of the SMD LED packages, which individually include the LEDs processed into the cavities. Consequently, such a COB LED display can include the LEDs in higher density.
For instance, an LED display disclosed in Patent Document 1 or 2 includes LEDs and columnar or convex lenses disposed on the individual LEDs. Such an LED display improves an orientation property, thereby increasing the efficiency of light use. Further, a different LED display disclosed in Patent Document 3 includes the following: a plurality of LEDs arranged on a substrate; a reflection plate having a plurality of holes corresponding one-to-one to the LEDs, the reflection plate being secured to the substrate while being aligned with the substrate; and a light-reflection case including a glass plate and disposed on the reflection plate. Consequently, such an LED display improves an orientation property and reduces the nonuniformity in luminance.